As long as your bankroll can handle putting more money on the table, and as long as you are a winning player, multi-tabling is worth trying. Personally, I was playing 2-3 tables from the very beginning. Less than 3 tables and I have to be watching a movie or something. (I really lack focus)
Think of it this way, it's usually safer to add a table at your current stakes than to move up to the next stakes. Just keep an eye on your BB/100 and make sure it isn't seriously affected by the additional table(s).
I've made the assumption that you're playing ring games. SNGs are a different breed entirely, and can be more difficult to multi-table.